1. Field of the Invention
The present invention relates to a chair chassis for improving supporting stability when the backrest of the chair is in a tilted state.
2. Description of the Related Art
FIG. 7 of the drawings illustrates a conventional chair comprising a base 1xe2x80x2, a support frame 2xe2x80x2, a seat 3xe2x80x2, and a backrest 4xe2x80x2. The base 1xe2x80x2 includes a post 11xe2x80x2 in a central area thereof. The support frame 2xe2x80x2 is formed by means of bending a metal tube and includes a bottom connected to the post 11xe2x80x2. The support frame 2xe2x80x2 further includes a connecting block 21xe2x80x2 on each of two sides thereof, with a positioning rod 22xe2x80x2 attached to each connecting block 21xe2x80x2. The backrest 4xe2x80x2 is connected to a rear of the support frame 2xe2x80x2 at two sections of the support frame 2xe2x80x2. The seat 3xe2x80x2 has a rear end connected to a bottom of the backrest 4xe2x80x2. Two sliding rods 31xe2x80x2 are respectively provided to undersides of two sides of the seat 3xe2x80x2 and extended through the connecting blocks 21xe2x80x2. When the backrest 4xe2x80x2 is tilted rearward, the seat 3xe2x80x2 shifts and the sliding rods 31xe2x80x2 are moved accordingly. Further, the positioning rods 22xe2x80x2 can be operated to be engaged with the sliding rods 31xe2x80x2 for retaining the backrest 4xe2x80x2 in the desired inclination angle.
However, when the backrest 4xe2x80x2 is tilted rearward, the backrest 4xe2x80x2 is not supported at its central area, failing to provide a stable support while the user lying his or her back in the backrest 4xe2x80x2. Further, the sliding rods 31xe2x80x2 respectively slide along the connecting blocks 21xe2x80x2 while the seat 3xe2x80x2 is moving such that the sliding rods 31xe2x80x2 are apt to shift from their normal position or the sliding rods 31xe2x80x2 are apt to bend and deform, causing the sliding rods 31xe2x80x2 to be stuck in the connecting blocks 21xe2x80x2. Further, the level of the seat 3xe2x80x2 is not adjustable and thus not suitable for users of different heights. Further, the support frame 2xe2x80x2 formed by means of bending cannot be folded after the chair is disassembled, causing inconvenience to transport and storage.
FIG. 8 of the drawings illustrates another conventional chair that includes a chassis 6xe2x80x2 attached to an underside of a seat 5xe2x80x2 and a backrest 7xe2x80x2 attached to a rear of the seat 5xe2x80x2. An elastic means 61xe2x80x2 is provided in the chassis 6xe2x80x2 so that the front end of the seat 5xe2x80x2 is moved upward when the backrest 7xe2x80x2 is tilted rearward. However, the center of gravity of the user sitting in the chair is moved rearward while the backrest 7xe2x80x2 is tilted rearward. As a result, the user might fall from the chair and thus be injured.
An object of the present invention is to provide a chair chassis for improving supporting stability by moving the seat forward when the backrest of the chair is in an inclined state.
Another object of the present invention is to provide a chair chassis that limits the maximum inclination angle of the backrest.
A further object of the preset invention is to provide a chair chassis allowing easy assembly and transport convenience.
A chair in accordance with the present invention includes:
a chair base;
a seat mounted on top of the chair base;
a backrest pivotally attached to a rear of the seat, the backrest including a support rod mounted thereon; and
a chassis mounted below the seat, the chassis including a base, a positioning mechanism, a movable member, and a support frame;
the base including a rear end fixedly connected to the support frame, the base including an intermediate portion for connection with the positioning mechanism, the base further including a front end on which two guide plates are mounted for connecting with a front end of the movable member, each guide plate having a guide slot;
the positioning mechanism including at least one positioning plate and a control rod, said at least one positioning plate being mounted to the base and including an end connected to a rear end of the movable member, a top having a hole defined therein, and an intermediate portion having a slot defined therein, the control rod controlling said at least one positioning plate to move between a loosened position and a tightening position for retaining the backrest in a desired inclination angle;
the movable member including an upper end fixed to the seat, a front axle rod being mounted to a front end of the movable member and extending through the guide slots of the guide plates of the base, a rear axle rod being mounted to a rear end of the movable member and extending through the hole of said at least one positioning plate;
the support frame including a bottom fixed to a rear end of the base and a top pivotally connected to the support rod of the backrest;
wherein when the backrest is tilted rearward, the seat moves forward and urges the movable member to shift, with the front axle rod sliding along the guide slots of the guide plates, and with said at least one positioning plate moving together with the rear axle rod.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.